Chemical compositions and their use as fuel additives

ABSTRACT

A compound of the general formula ##STR1## where X is CONR 2  or CO 2   -  + H 2  NR 2   
     Y and Z are the same or different and selected from the group consisting of CONR 2 ,CO 2  R, OCOR, --OR, --R, --NCOR and 
     one of Y or Z may be absent and 
     R is selected from the group consisting of alkyl, alkoxy alkyl or polyalkoxyalkyl preferably containing at least 10 carbon atoms in the main chain.

This is a division of application Ser. No. 867,850, filed Apr. 13, 1992now abandoned, which is a continuation of U.S. Ser. No. 673,842, filedMar. 19, 1991, now abandoned which is a continuation of U.S. Ser. No.366,155, f. Jun. 14, 1989, now abandoned which is a continuation in partof U.S. Ser. No. 281,939, f. Dec. 6, 1988, now abandoned, which is acontinuation of U.S. Ser. 136,726, f. Dec. 22, 1987, now abandoned.

This invention relates to new chemical compounds which are useful ascrystal modifiers in liquid hydrocarbons particularly fuels especiallydistillate fuels, the use of these chemicals as distillate fueladditives and to fuels containing the additives.

Long n-alkyl derivatives of difunctional compounds have previously beendescribed as has their use as wax crystal modifiers, to wit derivativesof alkenyl succinic acid (U.S. Pat. No. 3,444,082), maleic acid (U.S.Pat. No. 4,211,534) and phthalic acid (GB 2923645, U.S. Pat. Nos.4,375,973 and 4,402,708.

We have now found that certain novel compounds are useful as wax crystalmodifiers in distillate fuels making possible a significant reduction inthe size of the wax crystals formed to below 4000 nanometres sometimesbelow 2000 nanometres preferably below 1000 nanometres when themodifiers are used alone or in combination with other known wax crystalmodifiers.

The present invention therefore provides a compound of the generalformula ##STR2## where X is CONR₂ or CO₂ ⁻⁺ H₂ NR₂

Y and Z are the same or different and selected from the group consistingof CONR₂, CO₂ R, OCOR, --OR, --R, --NCOR and

one of Y or Z may be absent and

R is selected from the group consisting of alkyl, alkoxy alkyl orpolyalkoxyalkyl preferably containing at least 10 carbon atoms in themain chain.

The compounds of the present invention may be prepared by reactingpyromellitic dianhydride with amines, alcohols, quaternary ammoniumsalts etc. Where the compounds are the amides or amine salts they arepreferably of a secondary amine which has a hydrogen- andcarbon-containing group containing at least 10 carbon atoms. Such amidesor salts may be prepared by reacting the acid or anhydride with asecondary amine or alternatively by reacting an amine derivative with acarboxylic acid or anhydride thereof. Removal of water and heating aregenerally necessary to prepare the amides from the acids. Alternativelythe carboxylic acid may be reacted with an alcohol containing at least10 carbon atoms or a mixture of an alcohol and an amine.

When the compounds are used as fuel additives we prefer that R, contains10 to 30 preferable 10 to 22 carbon atoms, for example 14 to 20 carbonatoms and are preferably straight chain or branched at the 1 or 2position. The other hydrogen- and carbon-containing groups can beshorter e.g. less than 6 carbon atoms or may if desired have at least 10carbon atoms. Suitable alkyl groups include methyl, ethyl, propyl,hexyl, decyl, dodecyl, tetradecyl, eicosyl and docosyl (behenyl).

These compounds are especially useful as fuel additives especially formineral oils containing paraffin wax which have the characteristic ofbecoming less fluid as the temperature of the oil decreases. This lossof fluidity is due to the crystallisation of the wax into plate-likecrystals which eventually form a spongy mass entrapping the oil therein.The temperature at which the wax crystals begin to form being known asthe Cloud Point and the temperature at which the wax prevents the oilfrom pouring is the Pour Point.

It has long been known that various additives act as wax crystalmodifiers when blended with waxy mineral oils. These compositions modifythe size and shape of wax crystals and reduce the cohesive forcesbetween the crystals and between the wax and the oil in such a manner asto permit the oil to remain fluid at lower temperature

Various Pour Point depressants have been described in the literature andseveral of these are in commercial use. For example, U.S. Pat. No.3,048,479 teaches the use of copolymers of ethylene and C₁ -C₅ vinylesters, e.g. vinyl acetate, as pour depressants for fuels, specificallyheating oils, diesel and jet fuels. Hydrocarbon polymeric pourdepressants based on ethylene and higher alpha-olefins, e.g. propylene,are also known.

U.S. Pat. No. 3,961,916 teaches the use of a mixture of copolymers, tocontrol the size of the wax crystals and United Kingdom Patent 1,263,152suggests that the size c the wax crystals may be controlled by using acopolymer having a low degree of side chain branching. Both systemsimprove the ability of the fuel to pass through filters as determined bythe Cold Filter Plugging Point (CFPP) test since instead of plate likecrystals formed without the presence of additives the needle shaped waxcrystals produced will not block the pores of the filter rather forminga porous cake on the filter allowing passage of the remaining fluid.

Other additives have also been proposed for example, United KingdomPatent 1,469,016, suggest that the copolymers of di-n-alkyl fumaratesand vinyl acetate which have previously been used as pour depressant forlubricating oils may be used as co-additives with ethylene/vinyl acetatecopolymers in the treatment of distillate fuels with high final boilingpoints to improve their low temperature flow properties.

U.S. Pat. No. 3,252,771 relates to the use of polymers of C₁₆ to C₁₈alpha-olefins obtained by polymerising olefin mixtures that predominatein normal C₁₆ to C₁₈ alpha-olefins with aluminium trichloride/alkylhalide catalysts as pour depressants in distillate fuels of the broadboiling, easy-to-treat types available in the United States in the early1960's.

It has also been proposed to use additives based on olefin/maleicanhydride copolymers. For example, U.S. Pat. No. 2,542,542 usescopolymers of olefins such as octadecene with maleic anhydrideesterified with an alcohol such as lauryl alcohol as pour depressantsand United Kingdom Patent 1,468,588 uses copolymers of C₂₂ -C₂₈ olefinswith maleic anhydride esterified with behenyl alcohol as co-additivesfor distillate fuels.

Similarly, Japanese Patent Publication 5,654,037 uses olefin/maleicanhydride copolymers which have been reacted with amines as pour pointdepressants and in Japanese Patent Publication 5,654,033 the derivativesof the olefin/maleic anhydride copolymers are used together withconventional middle distillate flow improvers such as ethylene vinylacetate copolymers.

Japanese Patent Publication 5,540,640 discloses the use of olefin/maleicanhydride copolymers (not esterified) and states that the olefins usedshould contain more than 20 carbon atoms to obtain CFPP activity.

United Kingdom 2,192,012 uses mixtures of esterified olefin/maleicanhydride copolymers and low molecular weight polyethylene, theesterified copolymers being ineffective when used as sole additives. Thepatent specifies that the olefin should contain 10-30 carbon atoms andthe alcohol 6-28 carbon atoms with the longest chain in the alcoholcontaining 22-40 carbon atoms.

U.S. Pat. Nos. 3,444,082; 4,211,534; 4,375,973 and 4,402,708 discussedpreviously suggest the use of certain nitrogen containing compounds.

The improvement in CFPP activity achieved by the incorporation of theadditives of these Patents is achieved by modifying the size and shapeof the wax crystals forming to produce needle like crystals generally ofparticle size 10 microns or bigger typically 30 to 100 microns. Inoperation of diesel engines or heating systems at low temperatures,these crystals do not generally pass through the filters but form apermeable cake on the filter allowing the liquid fuel to pass, the waxcrystals will subsequently dissolve as the engine and the fuel heats up,which can be by the bulk fuel being heated by recycled fuel. This can,however, result in the wax crystals blocking the filters, leading tostarting problems and problems at the start of driving in cold weatheror failure of fuel heating systems.

We have found that by using the compounds of the present inventionparticularly small wax crystals may be obtained which will pass throughthe filters of typical diesel engines and heating systems rather thanforming a cake on the filter. We also find that the use enhances theformation of nodular crystals which are desirable for creating permeablewax filter cakes.

The amount of the compound added to the distillate fuel oil ispreferably 0.001 to 0.5 wt. %, for example 0.01 to 0.10 wt. % based onthe weight of fuel.

The compound may conveniently be dissolved in a suitable solvent to forma concentrate of from 20 to 90, e.g. 30 to 80 weight % in the solvent.Suitable solvents include kerosene, aromatic naphthas, minerallubricating oils etc.

The use of the additives of this invention allows distillate fuel oilboiling in the range 120° C. to 500° C. and which has a wax content ofat least 0.5 wt. % at a temperature of 10° C. below the wax appearancetemperature, to be produced with wax crystals having an average particlesize less than 4000 nanometres, sometimes less than 2000 nanometres anddepending on the fuel, the crystals can be submicron size.

The Wax Appearance Temperature (WAT) of the fuel is measured bydifferential scanning calorimetry (DSC). In this test a small sample offuel (25 ul) is cooled at 2°C./minute together with a reference sampleof similar thermal capacity but which will not precipitate wax in thetemperature range of interest (such as kerosene). An exotherm isobserved when crystallisation commences in the sample. For example theWAT of the fuel may be measured by the extrapolation technique on theMettle PA 20003.

The wax content is derived from the DSC trace by integrating the areaenclosed by the baseline and the exotherm down to the specifiedtemperature. The calibration having been previously performed on a knownamount of crystallizing wax.

The wax crystal average particle size is measured by analysing aScanning Electron Micrograph of a fuel sample at a magnification of 4000to 8000× and measuring the longest axis of 50 crystals over apredetermined grid. We find that providing the average size is less than4000 nanometres the wax will begin to pass through the typical paperfilters used in diesel engines together with the fuel although we preferthat the size be below 3000 nanometres, more preferably below 2000 andmost preferably below 1000 nanometres, the actual size attainabledepends upon the original nature of the fuel and the nature and amountof additive used but we have found that these sizes and smaller areattainable.

The ability to obtain such small wax crystals in the fuel showssignificant benefit in diesel engine operability as shown by pumpingfuel that has been previously stirred (to remove settled wax effects)through a diesel filter at from 8 to 15 ml/second and 1.0 to 2.4 litersper minute per square metre of filter surface area at a temperature atleast 5° C. below the wax appearance temperature with at least 1 wt. %of the fuel being present in the form of solid wax. Both fuel and waxare considered to successfully pass through the filter if one or more ofthe following criteria are satisfied:

(i) when 18 to 20 liters of fuel have passed through the filter thepressure drop across the filter does not exceed 50 KPa, preferably 25KPa, more preferably 10 KPa, most preferably 5 KPa.

(ii) At least 60%, preferably at least 80%, more preferably at least 90wt. % of the wax present in the fuel, as determined by the DSC test isfound to be present in the fuel leaving the filter.

(iii) Whilst pumping 18 to 20 liters of fuel through the filter, theflow rate always remains at above 60% of the initial flow rate andpreferably above 80%.

These fuels containing the compounds of this invention have outstandingbenefits compared to previous distillate fuels improved in their coldflow properties by the addition of conventional additives. For examplethe fuels are operable at temperatures approaching the pour point andnot restricted by the inability to pass the CFPP test. Hence these fuelseither pass the CFPP test at significantly lower temperatures or obviatethe need to pass that test. The fuels also have improved cold startperformance at low temperatures since they do not rely on recirculationof warm fuel to dissolve undesirable wax deposits.

The best effect is usually obtained when the compounds of the inventionare used in combination with other additives known for improving thecold flow properties of distillate fuels generally, although they may beused on their own.

The compounds are preferably used together with what are known as combpolymers which have the general formula ##STR3## where D=R, CO.OR,OCO.R, R'CO.OR or OR

E=H or CH₃ or D or R'

G=H, or D

m=1.0 (homopolymer) to 0.4 (mole ratio)

J=H, R', Aryl or Heterocyclic group, R'CO.OR

K=H, CO.OR', OCO.R', OR', CO₂ H

L=H, R', CO.OR', OCO.R', Aryl, CO₂ H

n=0.0 to 0.6 (mole ratio)

R≧C₁₀

R'≧C₁

Another monomer may be terpolymerized if necessary.

Examples of suitable comb polymers are the fumarate/vinyl acetateparticularly those described in our European Patent applications0153176, 0153177, 85301047 and 85301048 and esterified olefine/maleicanhydride copolymers and the polymers and copolymers of alpha olefinesand esterified copolymers of styrene and maleic anhydride.

Examples of other additives with which the compounds of the presentinvention may be used are the polyoxyalkylene esters, ethers,ester/ethers and mixtures thereof, particularly those containing atleast one, preferably at least two C₁₀ to C₃₀ linear saturated alkylgroups and a polyoxyalkylene glycol group of molecular weight 100 to5,000 preferably 200 to 5,000, the alkyl group in said polyoxyalkyleneglycol containing from 1 to 4 carbon atoms. These materials form thesubject of European Patent Publication 0,061,895 A2. Other suchadditives are described in U.S. Pat. No. 4,491,455.

The preferred esters, ethers or ester/ethers which may be used may bestructurally depicted by the formula:

    R--0(A)--0--R"

where R and R"are the same or different and may be ##STR4## the alkylgroup being linear and saturated and containing 10 to 30 carbon atoms,and A represents the polyoxyalkylene segment of the glycol in which thealkylene group has 1 to 4 carbon atoms, such as polyoxymethylene,polyoxyethylene or polyoxytrimethylene moiety which is substantiallylinear; some degree of branching with lower alkyl side chains (such asin polyoxypropylene glycol) may be tolerated but it is preferred theglycol should be substantially linear, A may also contain nitrogen.

Suitable glycols generally are the substantially linear polyethyleneglycols (PEG) and polypropylene glycols (PPG) having a molecular weightof about 100 to 5,000, preferably about 200 to 2,000. Esters arepreferred and fatty acids containing from 10 -30 carbon atoms are usefulfor reacting with the glycols to form the ester additives and it ispreferred to use a C₁₈ -C₂₄ fatty acid, especially behenic acids. Theesters may also be prepared by esterifying polyethoxylated fatty acidsor polyethoxylated alcohols.

Polyoxyalkylene diesters, diethers, ether/esters and mixtures thereofare suitable as additives with diesters preferred for use in narrowboiling distillates whilst minor amounts of monoethers and monoestersmay also be present and are often formed in the manufacturing process.It is important for additive performance that a major amount of thedialkyl compound is present. In particular, stearic or behenic diestersof polyethylene glycol, polypropylene glycol orpolyethylene/polypropylene glycol mixtures are preferred.

The compounds of this invention may also be used with ethyleneunsaturated ester copolymer flow improvers. The unsaturated monomerswhich may be copolymerised with ethylene include unsaturated mono anddiesters of the general formula: ##STR5## wherein R₆ is hydrogen ormethyl, R ₅ is a --OOR₈ group wherein R₈ is hydrogen formate or a C₁ toC₂₈, more usually C₁ to C₁₇, and preferably a C₁ to C₈, straight orbranched chain alkyl group; or R₅ is a --COOR₈ group wherein R₈ is aspreviously described but is not hydrogen and R₇ is hydrogen or --COOR₈as previously defined. The monomer, when R6 and R₇ are hydrogen and R5is --OOCR₈, includes vinyl alcohol esters of C₁ to C₂₉, more usually C₁to C5, monocarboxylic acid, and preferably C₂ to C₂₉, more usually C₁ toC5 monocarboxylic acid, and preferably C₂ to C₅ monocarboxylic acid.Examples of vinyl esters which may be copolymerised with ethyleneinclude vinyl acetate, vinyl propionate and vinyl butyrate orisobutyrate, vinyl acetate being preferred. We prefer that thecopolymers contain from 5 to 40 wt. % of the vinyl ester, morepreferably from 10 to 35 wt. % vinyl ester. They may also be mixtures oftwo copolymers such as those described in U.S. Pat No. 3,961,916. It ispreferred that these copolymers have a number average molecular weightas measured by vapour phase osmometry of 1,000 to 10,000, preferably,1,000 to 5,000.

The compounds of the invention may also be used in distillate fuels incombination with other polar compounds, either ionic or non-ionic, whichhave the capability in fuels of acting as wax crystal growth inhibitors.Polar nitrogen containing compounds have been found to be especiallyeffective when used in combination with the glycol esters, ethers orester/ethers and such three component mixtures are within the scope ofthe present invention. These polar compounds are generally amine saltsand/or amides formed by reaction of at least one molar proportion ofhydrocarbyl substituted amines with a molar proportion of hydrocarbylacid having 1 to 4 carboxylic acid groups or their anhydrides;ester/amides may also be used containing 30 to 300, preferably 50 to 150total carbon atoms. These nitrogen compounds are described in U.S. Pat.No. 4,211,534. Suitable amines are usually long chain C₁₂ -C₄₀ primary,secondary, tertiary or quaternary amines or mixtures thereof but shorterchain amines may be used provided the resulting nitrogen compound is oilsoluble and therefore normally containing about 30 to 300 total carbonatoms. The nitrogen compound preferably contains at least one straightchain C₈ to C40, preferably C₁₄ to C₂₄ alkyl segment.

Suitable amines include primary, secondary, tertiary or quaternary, butpreferably are secondary. Tertiary and quaternary amines can only formamine salts. Examples of amines include tetradecyl amine, cocoamine,hydrogenated tallow amine and the like. Examples of secondary aminesinclude dioctacedyl amine, methyl-behenyl amine and the like. Aminemixtures are also suitable and many amines derived from naturalmaterials are mixtures. The preferred amine is a secondary hydrogenatedtallow amine of the formula HNR₁ R₂ where in R₁ and R₂ are alkyl groupsderived from hydrogenated tallow fat composed of approximately 4% C₁₄,31% C₁₆, 59% C₁₈.

Examples of suitable carboxylic acids and their anhydrides for preparingthese nitrogen compounds include cyclohexane, 1,2 dicarboxylic acid,cyclohexene, 1,2-dicarboxylic acid, cyclopentane 1,2 dicarboxylic acid,naphthalene dicarboxylic acid and the like. Generally, these acids willhave about 5-13 cabon atoms in the cyclic moiety. Preferred acids usefulin the present invention are benzene dicarboxylic acids such as phthalicacid, isophthalic acid, and terephthalic acid. Phthalic acid or itsanhydride is particularly preferred. The particularly preferred compoundis the amide-amine salt formed by reacting 1 molar portion of phthalicanhydride with 2 molar portions of di-hydrogenated tallow amine. Anotherpreferred compound is the diamide formed by dehydrating this amide-aminesalt.

Hydrocarbon polymers may also be used as part of the additivecombination which may be represented with the following general formula:##STR6## where T=H or R'

U=H, T or Aryl

v=1.0 to 0.0 (mole ratio)

w=0.0 to 1.0 (mole ratio)

where R¹ is alkyl.

These polymers may be made directly from ethylenically unsaturatedmonomers or indirectly by hydrogenating the polymer made from monomerssuch as isoprene, butadiene etc.

A particularly preferred hydrocarbon polymer is a copolymer of ethyleneand propylene having an ethylene content preferably between 20 and 60%(w/w) and is commonly made via homogenous catalysis.

The Additives of the present invention may also be used in combinationwith the sulpho carboxy materials described in our application U.S. Ser.No. 324,598 which claims use of compounds of the general formula:##STR7## where A and B may be the same or different and may be alkyl,alkenyl or aryl;

L is selected from the group consisting of

>CH--CH< and

>C═C< and

A, B and L together can constitute part of a cyclic structure which canbe aromatic, alicyclic or mixed aromatic/alicyclic, and with the provisothat the groups --X--X¹ and Y--Y¹ are located on different carbon atomsconstituting L and in that when A, B and L do not constitute part of acyclic structure one of A or B may be hydrogen and in that when L isnon-cyclic ethylenic, said X--X¹ and Y--Y¹ groupings are present in acis configuration;

X is selected from the group consisting of

SO₃.sup.(-), --C(O)--, --C(O)O.sup.(-), --R⁴ --C(O)--, --NR³ C(O)----R⁴O--, --R⁴ OC(O)--, --R⁴ -- and --NC(O)--;

X¹ is selected from the group consisting of

N⁺ R₃ ³ R¹, N⁺ HR₂ ³ R¹, H₂ N⁺ R³ R¹, H₃ N⁺ R¹, --NR³ R¹, and R¹ ;

Y is --SO₃.sup.(-) or --SO₂ ;

when Y is SO₃ (-) y¹ is selected from the group consisting of N.sup.(+)R₂ ³ R², HN.sup.(+) R₂ ³ R², H₂ N.sup.(+) R³ R² and H₃ N.sup.(+) R²

and when Y is --SO₂ -- yl is --OR², --NR³ R² or --R²

and wherein R¹ and R² are independently selected from the groupconsisting of alkyl alkoxy alkyl or polyalkoxyalkyl groups containing atleast 10 carbon atoms in their chain;

R³ is hydrocarbyl and each R³ may be same or different; and

R⁴ is --(CH₂)_(n) where n is from 0 to 5.

Multicomponent additive systems may be used and the ratios of additivesto be used will depend on the fuel to be treated.

The additive systems which form part of the present invention mayconveniently be supplied as concentrates for incorporation into the bulkdistillate fuel. These concentrates may also contain other additives asrequired. These concentrates preferably contain from 3 to 75 wt. %, morepreferably 3 to 60 wt. %, most preferably 10 to 50 wt. % of theadditives preferably in solution in oil. Such concentrates are alsowithin the scope of the present invention. The additives of thisinvention may be used in the broad range of distillate fuels boiling inthe range 120° to 500° C.

The invention is illustrated by the following Examples.

PREPARATION Example 1 Additive X

The 1,2,4,5 tetra, N,N di(hydrogenated tallow) amido benzene wasprepared by reacting 4 moles of dihydrogenated tallow amine with onemole of pyromellitic dianhydride in the melt at 225° C. in a flaskcontaining a stirrer, temperature probes, Nitrogen pruge anddistillation condenser. Water was distilled out for approximately 8hours and the product obtained.

The product was analysed by Infra Red and 500 MHz Nuclear MagneticResonance Spectroscopy and the spectra which is attached hereto as FIGS.1 and 2 confirmed the structure to be a mixture of the tetraamide,triamide/mono salt and diamide/disalt in the following ratios: 44: 37:19 respectively.

Additive Y

The pyromellitic dianhydride (1 mole) was reacted with 2 moles of Alfol2022 a mixture of n-alkyl alcohols (n C₁₈ 7% max, n C₂₀ 58% min, n C₂₂30% min and n C₂₄ 6% max), at 120° C. for 2 hours in the absence of anysolvent. 2 moles of dihydrogenated tallow amine was then added to thereaction mixture, the temperature elevated to 150° C. and the reactioncontinued for another 2 hours. The final product having 2 functionalgroups esterified and the other 2 aminated (i.e. in the form of amide orcarboxylate/dialkyl ammonium salt).

Testing

The effectiveness of the product of Example 1 in additive systems toimprovers filterability of distillate fuels were determined by thefollowing methods.

The flow improver Extended Programmed Cooling Test (XPCT) which is aslow cooling test designed to indicate whether the wax in the fuel willpass through filters such as are found in heating oil distributionsystem.

In the test, the cold flow properties of the described fuels containingthe additives were determined as follows. 300 ml. of fuel are cooledlinearly at 1° C./hour to the test temperature and the temperature therheld constant. After 2 hours at -9° C., approximately 20 ml. of thesurface layer is removed as the abnormally large wax crystals which tendto form on the oil/air interface during cooling. Wax which has settledin the bottle is dispersed by gentle stirring, then a Cold FilterPlugging Point CFPP filter assembly which is described in detail in"Journal of the Institute of Petroleum", Volume 52, Number 510, Jun.1966, pp. 173-285 is inserted. The tap is opened to apply a vacuum of500 mm. of mercury and closed when 200 ml. of fuel have passed throughthe filter into the graduated receiver. A PASS is recorded if the 200ml, will pass through a given mesh size or a FAIL if the filter hasbecome blocked.

A series of CFPP filter assemblies with filter screens of 10 um to 45 umincluding LTFT (AMS 100.65) and a Volzwagen Tank filter (part no.KA/4-270/65.431-201-511) both intermediate between 30 and 40 um are usedto determine the finest mesh the fuel will pass.

Wax settling studies were also performed prior to PCT filtration. Theextent of the setled layer was visually measured as a % of the totalfuel volume. Thus extensive wax settling would be given by a low numberwhilst an unsettled fluid fuel would be at a state of 100%. Care must betaken because poor samples of gelled fuel with large wax crystals almostalways exhibit high values, therefore these results should be recordedas "gel".

The following additives were used

i) Additive A

Al was a mixture of two ethylene-vinyl acetate copolymers, 3 parts byweight of one consisting of ethylene and about 36 wt. % vinyl acetate,and has a number average molecular weight of about 1800 (VPO) and onepart by weight of A2.

A2 consists of a polymer containing 13.5 wt. % vinyl acetate and has anumber average molecular weight of 3500 (VPO).

(ii) Additive B

A copolymer of ethylene and propylene containing 56 wt. % ethylene andof number average molecular weight of 50,000.

(iii) Additive C

D was made esterifying a 1:1 molar styrene-maleic anhydride copolymerwith 2 moles of C₁₄ H₂₉ OH per mole of anhydride groups were used in theesterification (slight excess, 5% alcohol used) step using p-toluenesulphonic acid as the catalyst (1/10 mole) in xylene solvent, which gavea molecular weight (Mn) of 50,000 and contained 3% (w/w) unreactedalcohol.

(iv) Additive D

N N dihydrogenated tallow ammonium salt of 2N N¹ dihydrogenated tallowbenzene sulphonate.

(v) Additive E

E was made by polymerizing a 1:1 (molar) mixture of styrene anddi-n-tetradecyl fumarate in cycohexane under the following conditions.Di-T-butyl peroctate was used as an initiator, 20% of the styrene wascharged initially with all of the fumarate and the remaining 80% of thestyrene was charged over one hour. After this time a soak period offifteen minutes was used. The pressure was maintained at 80 psig withnitrogen and the polymerization temperature was 120° C.

Example 2

Characteristics of Fuel used

    ______________________________________                                        Distillation ASTM D-86(°C.)                                            ibp   20      50      90    fb.sub.p                                                                            CP(°C.)                                                                       WAP(°C.)                      ______________________________________                                        228   280     310     351   374   +5.0   0.0                                  ______________________________________                                    

An additive combination comprising 250 p.p.m. of each of Additive X,Additives B, C and D was included in the fuel and tested at -14° C. andthe fuel was found to pass with a 15 micron screen.

A comparative test using a mixture of 333 p.p.m. of each of additives B,C and D showed the finest mesh the fuel would pass was 35 to 40 microns.

Example 3

Fuel 1 was as described in the previous example and the seven otherfuels used had the following characteristics:

    ______________________________________                                                                    Cloud                                                     RATIO OF COMPONENTS Point                                             ______________________________________                                        FUEL BLEND                                                                              Kerosene LCGO    LGO    HGO   (°C.)                          ______________________________________                                        2         25       --      100    20    -3                                    3         12.5     12.5    100    20    -2                                    4         --       25      100    20    -2                                    5         --       --      100    10    -5                                    6         85       --      100    30    -4                                    7         42.5     42.5    100    30    -4                                    8         --       85      100    30    -4                                    ______________________________________                                        Component Characteristic                                                      Distillation ASTM-D86  Cloud                                                         ibp    20     50   90    fbp  Point  Density                           ______________________________________                                        Kerosine                                                                             152    184    200  226   240  -53    0.793                                                                  (freeze                                                                       point)                                   LCCO*  143    195    218  256   293  -72    0.869                                                                  (freeze                                                                       point)                                   LGO**  200    259    282  318   334  -8     0.847                             HGO*** 1.89   349    381  415   438  +20    0.883                             ______________________________________                                         *Light Cracked Gas Oil                                                        **Light Gas Oil                                                               ***Heavy Gas Oil   The Additive combinations used and the Test results ar     set out in the following Table 1.

                                      TABLE 1                                     __________________________________________________________________________                             Wax                           VW                     Additive                                                                           D  C  B  X   A2 A1  Settlement                                                                          10 um                                                                             15 um                                                                             20 um                                                                             25 um                                                                             35 um                                                                             LTFT                                                                              Filter                                                                            45                 __________________________________________________________________________                                                               um                 Fuel 1                                                                             250                                                                              250                                                                              250           100% but  150 ml                                                                            14.5 s                                                          Fluffy                                                                              50 s                                                250                                                                              250                                                                              250                                                                              250        50% Light                                                                           B   B   150 ml                                                                            12 s                                                                      20 s                                        250                                                                              250       250    100%  B   50 ml                                                                             150 ml                                                                            180 ml                                                                15 s                                                                              32 s                                                                              41 s                                    250                                                                              250   250 250    None  B   B   36 s                                                                          25 s                                        250   150                                                                              400    200 50% light                                                                           70 ml   11.9 s                                                                20 s                                           Fuel 2                                                                             250                                                                              250                                                                              250           10% thick                         B                                           25% light     B   30 ml                                                                             120 ml                                                                            30 ml                                                                             4.9 s                                                             5.7 s                                                                             15.3 s                                                                            6.6 s                           250                                                                              250       250    100%              B   80 ml                                                                             100 ml                                                                            6.3 s                                                                 7.6 s                                                                             8.1 s                           250                                                                              250   250 250    100%      B   70 ml                                                                             110 ml                                                                            11.4 s                                                                17 s                                                                              22 s                                    250   150                                                                              400    200 50% Light B   150 ml                                                                            9.4 s                                                                     28 s                                   Fuel 3                                                                             250                                                                              250                                                                              250           10% thick                         B                                           25% light         100 ml                                                                            2.6 s                                                                     16 s                                    250                                                                              250       250    100%                  60 ml                                                                             60 ml                                                                             6.9 s                                                                 85 s                                                                              6.9 s                           250                                                                              250   250 250    100%      B   100 ml                                                                            16.4 s                                                                    30 s                                        250   150                                                                              400    200 50% Light B   12.5 s                                 Fuel 4                                                                             250                                                                              250                                                                              250           20% light                         B                       250                                                                              250                                                                              250                                                                              250        100%      B   80 ml                                                                             27 s                                                                      15 s                                        250                                                                              250       250    100%          50 ml                                                                             100 ml                                                                            15 s                                                                  11 s                                                                              20 s                                    250                                                                              250   250 250    100%  B   50 ml                                                                             130 ml                                                                            40 s                                                                      11.5 s                                                                            25 s                                    250   150                                                                              400    200 25% Light                                                                           B   B   150 ml                                                                            10.5 s                                                                    24 s                                   Fuel 5                                                                             250                                                                              250                                                                              250           10% thick                         B                       250                                                                              250                                                                              250                                                                              250        25% light                         B                       250                                                                              250       250    100%                              B                       250                                                                              250   250 250    100%                          9.6 s                       250   150                                                                              400    200 100%                          50                                                                                Bl                                                                        15 s                   Fuel 6                                                                             250                                                                              250                                                                              250           10% thick                         B                                           90% clear                                                 250                                                                              250                                                                              250                                                                              250        25% light     50 ml                                                                             100 ml                                                                            7.6 s                                                                 12.4 s                                                                            12.2 s                                  250                                                                              250       250    100%          B   100 ml                                                                            7.6 s                                                                     9.6 s                                   250                                                                              250   250 250    100%  50 ml                                                                             120 ml                                                                            12.1 s                                                                9.2 s                                                                             19 s                                            250   150                                                                              400    200 50% light                                                                           150 ml  7.8 s               B                                                 35 s                                           Fuel 7                                                                             250                                                                              250                                                                              250           10% thick             B   B   6.3 s                                           90% clear                                                 250                                                                              250                                                                              250                                                                              250        100%  27 s                                                                          17 s                                                250                                                                              250       250    100%          B   120 ml                                                                            8.1 s                                                                     12.1 s                                  250                                                                              250   250 250    100%  120 ml                                                                            B   24 s                                                                  20 s                                                250   150                                                                              400    200 100%  18 s                                                                          30 s                                           Fuel 8                                                                             250                                                                              250                                                                              250           100%  48 s    8.4 s                                       250                                                                              250                                                                              250                                                                              250        100%  28 s                                                                          19 s                                                250                                                                              250       250    100%  B   100 ml                                                                            10 s                                                                      16 s                                            250                                                                              250   250 250    100%  100 ml                                                                            100 ml                                                                            17 s                                                                  16 s                                                                              18 s                                            250   150                                                                              400    200 100%  23 s                                                                          16 s                                           __________________________________________________________________________     Note                                                                          B = blocked mesh                                                              S = Volume passed in number of seconds                                        B means filter was blocked                                                    *S = Number of seconds for the specified volume to pass the filter 9.6 s 

Example 4

The ability of a Fuel 9 to pass through a diesel vehicle main filter wasdetermined in an apparatus consisting of a typical diesel vehicle mainfilter mounted in a standard housing in a fuel line; the Bosch Type asused in a 1980 VW Golf diesel passenger car, and a Cummins FF105 as usedin the Cummins NTC engine series are appropriate. A reservoir and feedsystem capable of supplying half a normal fuel tank of fuel linked to afuel injection pump as used in the VW Golf is used to draw fuel throughthe filter from the tank at constant flowrate, as in the vehicle.Instruments are provided to measure pressure drop across the filter, theflow rate from the injection pump and the unit temperatures. Receptaclesare provided to receive the pumped fuel, both `injected` fuel and thesurplus fuel.

In the test the tank is filled with 19 kilogrammes of fuel and leaktested. When satisfactory, the temperature is stabilised at an airtemperature 8° C. above fuel cloud point. The unit is then cooled at 1°C./hour to the desired test temperature, and held for 4 hours for fueltemperature to stabilise. The tank is vigorously shaken to fullydisperse the wax present; a sample is taken from the tank and 1 litre offuel removed through a sample point on the discharge line immediatelyafter the tank and returned to the tank. The pump is then started, withpump rpm set to equate to pump rpm at 110 kph road speed. In the case ofthe VW Golf, this is 1900 rpm, corresponding to an engine speed of 3800rpm. Pressure drop across the filter and flow rate of fuel from theinjection pump are monitored until fuel is exhausted, typically 30 to 35minutes.

The key measurements are:

Pressure drop across the main filter--always a paper filter, designed totrap particles of 5-10 microns length in the many layers of paperfibres. Typically, filter papers are either spirally wound orstar-shaped around a central core, with the paper about 150-300 micronsthick. Maximum pore sizes (or `gaps between fibres` at one level) areabout 100 microns, with the majority of `gaps` ranging from 1-30microns.

Wax settlement as measured in the previous Examples

Wax passage through the filter measured by differential scanningcalorimetry.

RESULTS

The additive formulations used are set out in Table 2, together with the`FULL PASSAGE LIMIT` or FPL deduced from the rig results.

`FULL PASSAGE` is defined as a run where the peak pressure drop neverrose above 10 kPa. This generally means that more than 90% of the wax inthe fuel flowed with the liquid fuel through the filter.

Fuel 9 had the following characteristics:

    ______________________________________                                        Distillation ASTM D-86 (°C.)                                           IBP  20%    50%    90%   FBP  Cloud Point (°C.)                                                                 WAP(°C.)                      ______________________________________                                        190  246    282    346   374  +3         0                                    ______________________________________                                    

It can be seen that by including Y or particularly X into the additivesystem, substantial benefits in vehicle performance may be obtained.

    ______________________________________                                        Additives (ppm)                                                                                                  Wax Settlement                                                                          FPL                              A1   A2     C      E     X    Y    %         (°C.)                     ______________________________________                                        1000 --     --     --    --   --   30         -9.sup.(1)                      --   250    250    250   --   --   None      -15.sup.(3)                      --   250    250    250   250  --   None      -25.sup.(2)                      --   250    250    250   --   250  None      -20                              ______________________________________                                         At -27° C. a failure was brought about by fuel viscosity even          though almost 100% of the crystals were passing through the filter       

We claim:
 1. A wax crystal modifier for distillate fuels boiling in therange of 120° to 500° C. comprising (a) at least one compoundrepresented by the structural formula: ##STR8## wherein X is selectedfrom the group consisting of --CON(R)₂, and --CO₂ ⁻⁺ H₂ N(R)₂ ; Y and Zare independently selected from the group consisting of --CON(R)₂, --CO₂R; and R is a C₁₀ to about C₃₀ alkyl, alkoxyalkyl or polyalkoxyalkyl;(b) at least one comb polymer, and (c) at least one polymer capable ofimproving the low temperature properties of said fuel selected fromcompounds of the formula: ##STR9## where A and B may be the same ordifferent and may be alkyl, alkenyl or aryl;L is selected from the groupconsisting of>CH--CH< and >C═C<and A, B and L together can constitutepart of a cyclic structure which can be aromatic, alicyclic or mixedaromatic/alicyclic, and with the proviso that the groups --X--X¹ andY--Y¹ are located on different carbon atoms constituting L and in thatwhen A, B and L do not constitute part of a cyclic structure one of A orB may be hydrogen and in that when L is non-cyclic ethylenic, said X--X1and Y--Y1 groupings are present in a cis configuration;X is selectedfrom the group consisting of --SO₃ (--), --C(O)--, --C(O)O(-), --R⁴--C(O)O--, --NR³ C(O)--R⁴ O--, --R⁴ OC(O)--, --R⁴ -- and --NC(O)--; X¹is selected from the group consisting of N.sup.(+) R₃ ³ R¹, N.sup.(+)HR₂ ³ R¹, H₂ N.sup.(+) R³ R¹, H₃ N.sup.(+) R¹, --NR³ R¹, and R¹ ; Y is--SO₃ (--) or --SO₂ ;when Y is SO₃ (--), Y¹ is selected from the groupconsisting of N.sup.(+) R₃ ³ R², HN.sup.(+) R₂ ³ R², H₂ N.sup.(+) R³ R²and H₃ N.sup.(+) R² and when Y is --SO₂ --, Y¹ is --OR², --NR³ R² or--R² and whereinR¹ and R² are independently selected from the groupconsisting of alkyl, alkoxy alkyl or polyalkoxyalkyl groups containingat least 10 carbon atoms in their chain; R³ is hydrocarbyl and each R³may be the same or different; and R⁴ is --(CH₂)_(n) where n is from 0 to5;polyoxyalkylene esters, ethers, ester/ethers and mixtures thereof; andethylene-unsaturated ester copolymers.
 2. The wax crystal modifier ofclaim 1 wherein X of (a) is --CON(R)₂.
 3. The wax crystal modifier ofclaim 1 wherein X of (a) is --CO₂ ⁻ +H₂ N(R)₂.
 4. The wax crystalmodifier of claim 1 wherein Y and Z of (a) are --CO₂ R.
 5. The waxcrystal modifier of claim 1 wherein Y of (a) is --CON(R)₂.
 6. A waxcontaining fuel composition comprising a distillate fuels boiling in therange of 120° to 500° C. and (a) a wax crystal modifying amount of atleast one compound represented by the structural formula: ##STR10##wherein X is selected from the group consisting of --CON(R)₂, and --CO₂⁻⁺ H₂ N(R)₂ ; Y and Z are independently selected from the groupconsisting of --CON(R)₂, --CO₂ R; and R is a C₁₀ to about C₃₀ alkyl,alkoxyalkyl or polyalkoxyalkyl; and (b) at least one comb polymer, and(c) at least one polymer capable of improving the low temperatureproperties of said fuel selected from compounds of the formula:##STR11## where A and B may be the same or different and may be alkyl,alkenyl or aryl;L is selected from the group consisting of>CH--CH<and >C═C<and A, B and L together can constitute part of a cyclicstructure which can be aromatic, alicyclic or mixed aromatic/alicyclic,and with the proviso that the groups --X--X¹ and Y--Y¹ are located ondifferent carbon atoms constituting L and in that when A, B and L do notconstitute part of a cyclic structure one of A or B may be hydrogen andin that when L is non-cyclic ethylenic, said X--X¹ and Y--Y¹ groupingsare present in a cis configuration;X is selected from the groupconsisting of SO₃ (--), --C(O)--, --C(O)O(--), --R⁴ --C(O)O--, --NR³C(O)--R⁴ O--, --R⁴ OC(O)--, --R⁴ -- and --NC(O)--; X¹ is selected fromthe group consisting of N.sup.(+) R₃ ³ R¹, N.sup.(+) HR₂ ³ R¹, H₂N.sup.(+) R³ R¹, H₃ N.sup.(+) R¹, --NR³ R¹, and R¹ ; Y is --SO₃ (--) or--SO₂ ;when Y is SO₃ (--), Y¹ is selected from the group consisting ofN.sup.(+) R₃ ³ R², HN.sup.(+) R₂ ³ R², H₂ N.sup.(+) R³ R² and H₃N.sup.(+) R² and when Y is --SO₂ --, Y¹ is --OR², --NR³ R² or --R² andwhereinR¹ and R² are independently selected from the group consisting ofalkyl, alkoxy alkyl or polyalkoxyalkyl groups containing at least 10carbon atoms in their chain; R³ is hydrocarbyl and each R³ may be thesame or different; and R⁴ is --(CH₂)_(n) where n is from 0 to5.;polyoxyalkylene esters, ethers, ester/ethers and mixtures thereof;and ethyleneunsaturated ester copolymers.
 7. The composition of claim 6wherein X of (a) is --CON(R)₂.
 8. The composition of claim 6 wherein Xof (a) is --CO₂ -+H₂ N(R)₂.
 9. The composition of claim 6 or 7 wherein Yand Z of (a) are --CO₂ R.
 10. The composition of claim 6 wherein Y of(a) is --CON(R)₂.
 11. The wax containing fuel composition of claim 6containing 0.001 to 0.5 wt. % of the wax crystal modifier of (a).
 12. Anadditive concentrate comprising an oil solution containing (a) 5 to 60wt. % of a compound of the structural formula: ##STR12## wherein X isselected from the group consisting of --CON(R)₂, and --CO₂ ⁻⁺ H₂ N(R)₂ ;Y and Z are independently selected from the group consisting of--CON(R)₂, --CO₂ R; and R is a C₁₀ to about C₃₀ alkyl, alkoxyalkyl orpolyalkoxyalkyl; (b) at least one comb polymer, and (c) at least onepolymer capable of improving the low temperature properties of said fuelselected from compounds of the formula: ##STR13## where A and B may bethe same or different and may be alkyl, alkenyl or aryl;L is selectedfrom the group consisting of>CH--CH< and >C═C<and A, B and L togethercan constitute part of a cyclic structure which can be aromatic,alicyclic or mixed aromatic/alicyclic, and with the proviso that thegroups --X--X¹ and Y--Y¹ are located on different carbon atomsconstituting L and in that when A, B and L do not constitute part of acyclic structure one of A or B may be hydrogen and in that when L isnon-cyclic ethylenic, said X--X1 and Y--Y1 groupings are present in acis configuration;X is selected from the group consisting of SO₃ (--),--C(O)--, --C(O)O(--), --R⁴ --C(O)O--, --NR³ C(O)--R⁴ O--, --R⁴ OC(O)--,--R⁴ -- and --NC(O)--; X¹ is selected from the group consisting ofN.sup.(+) R₃ ³ R¹, N.sup.(+) HR₂ ³ R¹, H₂ N.sup.(+) R³ R¹, H₃ N.sup.(+)R¹, --NR³ R¹, and R¹ ; Y is --SO₃ (--) or --SO₂ ;when Y is SO₃ (--), Y¹is selected from the group consisting of N.sup.(+) R₃ ³ R², HN.sup.(+)R₂ ³ R², H₂ N.sup.(+) R³ R² and H₃ N.sup.(+) R² and when Y is --SO₂ --,Y¹ is --OR², --NR³ R² or --R² and whereinR¹ and R² are independentlyselected from the group consisting of alkyl, alkoxy alkyl orpolyalkoxyalkyl groups containing at least 10 carbon atoms in theirchain; R³ is hydrocarbyl and each R³ may be the same or different; andR⁴ is --(CH₂)_(n) where n is from 0 to 5.;polyoxyalkylene esters,ethers, ester/ethers and mixtures thereof; and ethylene-unsaturatedester copolymers.